Charged particle beam apparatus and method for operating the same

ABSTRACT

A charged particle beam apparatus is provided which comprises a charged particle source for producing a primary beam of charged particles, aperture means for collimating said primary beam of charged particles, wherein said aperture means is adapted to switch between a collimation of said primary beam to a width appropriate for serial imaging of a sample as well as a collimation of said primary beam to a width appropriate for parallel imaging of said sample, a condenser lens for condensing said primary beam of charged particles, scanning means for deflecting said primary beam of charged particles, an objective lens for focusing said condensed primary beam, a sectorized detector for detecting a secondary charged particles. Also, several different operation modes of the beam apparatus are described allowing for serial imaging as well as parallel imaging.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of European Patent Application No. 03001 048.2, filed Jan. 17, 2003, which is herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a charged particle beam apparatus and amethod for operating the same, especially the present invention relatesto an electron microscope which may be operated in different modes ofoperation allowing to switch from a serial imaging mode to a parallelimaging mode and vice versa.

2. Description of the Related Art

A variety of methods have been used to examine microscopic surfacestructures of semiconductors. These have important applications in thefield of semiconductor chip fabrication, where microscopic defects at asurface layer make the difference between a good or bad chip. Holes orvias in an intermediate insulating layer often provide a physicalconduit for an electrical connection between two outer conductinglayers. If one of these holes or vias becomes clogged, it will beimpossible to establish this electrical connection and the whole chipmay fail. Examination of microscopic defects on the surface of thesemiconductor layers is necessary to ensure quality control of thechips.

Charged particle beams have several advantages over other mechanisms toexamine samples. Light beams have an inherent resolution limit of about100 nm to 200 nm, but electron beams can investigate feature sizes assmall as a few nanometers. Electron beams are manipulated fairly easilywith electrostatic and electromagnetic elements, and are easier toproduce and manipulate than x-rays.

A variety of approaches involving charged particle beams have beenutilized for examining surface structure. In scanning electronmicroscopy (SEM), a narrow beam of primary electrons is raster-scannedacross the surface of a sample, also called the working plane. Primaryelectrons in the scanning beam cause the sample surface to emitsecondary or backscattered electrons. Because the primary electrons inthe beam of scanning electron microscopy are near a particular knownelectron energy there is a reduced corresponding charge build-up problemin SEM when compared to other inspection methods, and the surface of thesample remains substantially neutral. However, raster scanning a surfacewith scanning electron microscopy is slow because each pixel on thesurface is collected sequentially. In this context, a pixel may beunderstood as the diameter of the primary beam on the surface of thesample. However, other definitions may apply more properly for differentgeometries. Moreover, a complex and expensive electron beam steeringsystem is needed to control the beam pattern.

Another approach called Secondary Electron Emission Microscopy (SEEM)can be much faster than SEM because SEEM does not scan a narrow beamacross the sample, but instead directs a relatively wide beam ofelectrons at the surface. To put this in numerical perspective, the spotsize of the scanning beam in Scanning Electron Microscopy (SEM) istypically about 5 nm to 100 nm. The area illuminated by the incidentbeam in conventional Secondary Electron Emission Microscopy (SEEM) isabout 1 mm to 10 mm. Thus, the area illuminated by the beam inconventional SEEM is on the order of 10⁹ to 10¹² times larger than inSEM. Accordingly, SEEM is able to look at a larger surface more rapidlythan it is possible in SEM and, in this context, is therefore consideredas a parallel imaging method. The primary electron energies in SEEM areclose to the point used in SEM, i.e. about 0.5 to 1 keV. Such a SEEMdevice is described in U.S. Pat. No. 5,973,323 (Adler et al.).

The comparative speed advantage in SEEM, i.e. the maximum pixel rate, islimited mainly by the exposure time and the current density. The minimumexposure time that a beam must spend looking at a given image isdetermined by the acceptable Signal-to-Noise ratio of the image. Themaximum current density is determined by such practical considerationsas available gun brightness and possible sample damage, but also byelectron-electron interaction. Because the focused beam of primaryelectrons in SEM must scan the beam across the entire surface to beinspected, the maximum practical pixel rate in Scanning ElectronMicroscopy is less than or equal to 100 million pixels/second (100 MHz).In Secondary Electron Emission Microscopy (SEEM), a largetwo-dimensional area of the sample is imaged in parallel without theneed for scanning. The maximum pixel rate in SEEM is at leasttheoretically greater than 800 million pixels/second (800 MHz). Theexposure time of the beam in SEEM may correspondingly be much longerthan in SEM, and this permits a much lower current density while stillmaintaining a high Signal-to-Noise ratio. Thus, SEEM has the capabilityof investigating more sensitive sample surface structures whilerequiring lower brightness electron beam sources

Another approach is called Photo-Electron Emission Microscopy (PEM orPEEM), in which photons are directed at the surface of a sample to bestudied, and by the photoelectric effect electrons are emitted from thesurface. On an insulating surface, the emission of these electrons,however, may produce a net positive charge on the sample surface sincethere is a net flux of electrons from the surface. The sample continuesto charge positively until there are no emitted electrons, or electricalbreakdown occurs. This charge build-up problem may limit the utility ofPEEM for imaging insulators. However, depending on the material of thesample, an opposite effect may occur in PEEM, namely that a surfaceconductance is generated by the incident photons. The mechanismunderlying this effect is that of pair production of electrons andholes, so-called excitons, that are generated by the photons, therebygenerating enhanced surface conductance of the sample. Thus, electricalcharge may be transported away from the region of the incident lightbeam.

Another method of examining surfaces with electron beams is known as LowEnergy Electron Microscopy (LEEM), in which a relatively wide beam oflow-energy electrons is directed to be incident upon the surface of thesample, and electrons reflected from the sample are detected. However,LEEM suffers from a similar charge build-up problem since electrons aredirected at the sample surface, but not all of the electrons areenergetic enough to leave the surface. In LEEM, negatively-chargedelectrons accumulate on the surface, which repels further electrons fromstriking the sample, resulting in distortions and shadowing of thesurface. In LEEM, it may pose a problem that the surface chargesnegatively due to the low electron energies.

TAB. 1 below is a chart summarizing the differences between, andadvantages of, the four SEM, SEEM, PEEM and LEEM techniques:

TABLE 1 Differences between, and advantages of, the four SEM, SEEM, PEEMand LEEM techniques Secondary Photo- Low Scanning Electron ElectronEnergy Electron Emission Emission Emission Microscopy MicroscopyMicroscopy Microscopy (SEM) (SEEM) (PEEM) (LEEM) Incident ElectronsElectrons Photons Low- Particles Energy Electrons Detected SecondarySecondary Photo- Reflected Particles Electrons Electrons ElectronsElectrons Imaging Raster Parallel Parallel Parallel Method ScanningImaging Imaging Imaging Charging Limited Limited Positive NegativeCharging Charging Charge Charge Build-Up Build-Up

In Scanning Electron Microscopy (SEM), raster scanning imaging must beutilized which leads to a relatively low throughput because the electronbeam is focused to a narrow spot size. SEM, however, produces energeticprimary electrons incident at an energy of 0.5 to 1 keV, so that arelatively charge-neutral operation is attained. Energetic primaryelectrons produce secondary electrons in SEM.

In the Secondary Electron Emission Microscopy (SEEM) technique, a beamof energetic primary electrons is directed at the sample surface with anenergy of about 0.5 to 1 keV. Because a relatively wide beam of primaryelectrons is introduced, parallel imaging becomes possible, which issignificantly faster than SEM imaging. Moreover, the sample remainscharge neutral.

PEEM uses photons instead of primary electrons to produce emittedsecondary electrons. PEEM may suffer from the problem of positive chargebuild-up on insulating sample target materials because secondaryelectrons are being knocked off the sample surface by the photons, butno negatively charged particles replace these secondary electrons. Theinspecting photon beam of PEEM can be wide, and parallel imaging can beachieved.

In Low Energy Electron Microscopy (LEEM), a wide beam of primaryelectrons is projected at the inspection surface, and parallel imagingcan be achieved. These primary electrons are relatively low in energy,and the imaging method involves reflecting these low-energy electronsfrom the surface. Because only low energy electrons are incident,primary electrons are reflected but few secondary electrons are emitted.Also, the low energy implies a negative charge build-up because some ofthe electrons may be energetic enough to enter the sample but are notsufficiently energetic to escape the sample surface.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved electron beam apparatus which overcomes at least part of theproblems mentioned above. It is also an object of the present inventionto provide a method for operating the improved electron beam apparatus.

These objects are at least partly solved by an electron beam apparatusaccording to claims 1 and 4 and by a method according to claims 13, 14,15, 18 and 19.

Further advantages, features, aspects and details of the invention areevident from the dependent claims, the description and the accompanyingdrawings.

According to an embodiment of the present invention, a charged particlebeam apparatus is provided which comprises

-   -   a charged particle source for producing a primary beam of        charged particles,    -   aperture means for collimating said primary beam of charged        particles, wherein said aperture means is adapted to switch        between a collimation of said primary beam to a width        appropriate for serial imaging of a sample as well as a        collimation of said primary beam to a width appropriate for        parallel imaging of said sample,    -   a condenser lens for condensing said primary beam of charged        particles,    -   scanning means for deflecting said primary beam of charged        particles,    -   an objective lens for focusing said condensed primary beam,    -   a sectorized detector for detecting a secondary charged        particles.

This charged particle beam apparatus is capable of two different modesof operation: a first mode (SEM mode) in which the sample is scanned bya highly focused primary beam, and a second mode (SEEM mode) in whichthe sample is illuminated by a relatively wide primary beam forparallel, multi-pixel imaging. Thus, the apparatus provides thefunctions of both, a SEM and a SEEM, but within a single device.Accordingly, an apparatus according to the present embodiment requiresmuch less space and only a single vacuum pump means, compared to twosingle-functional prior art apparatus which are only capable of eitherSEM or SEEM. Further to this, the cost of purchase of an apparatusaccording to the present embodiment is much lower compared to thecombined costs of a conventional SEM and SEEM. Therefore, the apparatusaccording to the present embodiment of the invention is good value forusers which need the functions of a SEM as well as of a SEEM but not atthe same time.

According to a further embodiment of the present invention, a chargedparticle beam apparatus is provided which comprises

-   -   a charged particle source for producing a primary beam of        charged particles, a condenser lens for condensing said primary        beam of charged particles, aperture means for collimating said        primary beam of charged particles, scanning means for deflecting        said primary beam of charged particles, an objective lens for        focusing said condensed primary beam, wherein said objective        lens is adapted to switch between a focus forming an image of        said particle source in a plane of a surface of a sample to be        serially inspected and a focus forming an image of said aperture        means in a plane of a surface of a sample to be parallel        inspected, and a sectorized detector for detecting secondary        charged particles.

This charged particle beam apparatus is also capable of two differentmodes of operation: a first mode (SEM mode) in which the sample isscanned by a highly focused primary beam, and a second mode (SEEM mode)in which the sample is illuminated by a relatively wide primary beam forparallel, multi-pixel imaging. Accordingly, the apparatus according tothe present embodiment provides similar advantages as the apparatus tothe embodiment described above. Especially, homogeneous illumination andhigh current density are specific advantages of this embodiment. Theapparatus of the present embodiment utilizes an adapted objective lensto switch between SEM and SEEM mode wherein switching is accomplished byaltering the image plane of the objective lens. In SEM mode theobjective lens forms an image of the particle source or an intermediateimage of the particle source in the focal) plane, thus generating a beamhaving a very small width in the focal plane. In SEEM mode the objectivelens forms an image of the aperture in the focal plane. If the apertureis fully illuminated by the primary beam, a beam having a large width inthe focal plane of the objective lens is generated by this mode ofoperation. However, this is also dependent on the selected magnificationwhich is adjusted by the objective lens.

According to another embodiment of the present invention, the chargedparticle beam apparatus further comprises a light source for producing alight beam.

The provision of a light source allows additionally for Photo-ElectronEmission Microscopy (PEEM) to be accomplished in the present embodimentof the invention. As has been already mentioned above, PEEM may lead topositive charge build-up on insulating surfaces. However, SEEM may leadto negative charge build-up for the aforementioned reasons. Therefore,the apparatus according to the present embodiment may be operated in acombined SEEM/PEEM mode when inspecting insulating surfaces. In thiscombined SEEM/PEEM mode, the primary beam and the light beam may beadjusted such that the effects of negative/positive charge build-up oninsulating surfaces cancel each other and leave the surface in a stable,substantially uncharged state. Thus, also very sensitive structures maybe inspected with a largely reduced possibility of damaging them.Moreover, for other materials the incident light beam induces pairproduction of electrons and holes, thereby generating enhanced surfaceconductance. The excess charge built up by SEEM inspection could thus betransported away from the illuminated area on the sample surface.

According to an aspect of the present invention, a method for operatinga charged particle beam apparatus comprising a particle source, anaperture, an objective lens is provided, wherein said method comprisesthe steps of producing a charged particle beam, collimating said beam bysaid aperture, and focusing the beam by said objective lens, wherein animage of said aperture is formed on the surface of a sample to beinspected.

According to an aspect of the present invention, a method for operatingthe charged particle beam apparatus according to an embodiment of thepresent invention is provided, wherein the method of operation of thecharged particle beam apparatus is switched in operation between atleast two of modes SEM, SEEM, PEEM and SEEM/PEEM.

The above method allows to tap the full potential of the presentinvention in that a user may select different operation modes and applythem to the same sample without the need of transferring the sample to adifferent device for each respective mode of operation. Thus, aconsiderable amount of time and money can be saved since, e.g., thewhole device has to be evacuated just once.

BRIEF DESCRIPTION OF THE DRAWINGS

Some of the above indicated and other more detailed aspects of theinvention will be described in the following description and partiallyillustrated with reference to the figures. Therein:

FIG. 1 is a schematic drawing of an apparatus according to a firstembodiment of the present invention.

FIG. 2 is a top view of a multi aperture unit with several beam definingapertures arranged in a circle around the center beam defining aperturelocated in the middle of the circular plate.

FIG. 3 is a schematic drawing of the beam shaping section of the beamapparatus shown in FIG. 1 in the case where a multi aperture and firstand second deflection units are provided.

FIG. 4 shows the embodiment of FIG. 1 in a first mode of operation.

FIG. 5 shows the embodiment of FIG. 1 in a second mode of operationwherein also optional operation modes of the objective lens are shown.

FIG. 6 shows in a schematic way the principle of spatial resolution witha sectorized detector.

FIG. 7 is a schematic drawing of an apparatus according to a furtherembodiment of the present invention.

FIG. 8 shows the embodiment of FIG. 7 in a first mode of operation.

FIG. 9 shows the embodiment of FIG. 7 in a second mode of operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

It is to be understood within the context of the embodiments of thepresent invention that a charged particle beam is preferably an electronbeam. However, this should not be understood as limiting the scope ofthe present invention since also other charged particles like, e.g.protons or ions, can be used in an apparatus or method according to thepresent invention.

FIG. 1 shows an electron beam apparatus according to a first embodimentof the present invention. This apparatus comprises a electron source 1,which produces a primary beam of electrons during operation. Typicalelectron sources are filaments, e.g. made of tungsten, but can also beformed by micro emitter tips or arrays of those.

In some embodiments according to the present invention, an aperturemeans 2 is provided which is adapted to switch between two differentmodes of collimation, a serial imaging mode (SEM mode) and a parallelimaging mode (SEEM mode). In the specific embodiment shown in FIG. 1,the aperture means 2 is disposed below the electron source 1 tocollimate the electron beam to a desired width. Preferably, the primarybeam width appropriate for serial imaging has a width on the surface ofthe sample between 1 nm and 50 nm, and a primary beam width of about 2nm is especially preferred. These preferred primary beam widths allowfor excellent spatial resolution in the SEM mode. However, in theparallel imaging mode, the preferred primary beam width is between 0.5μm and 1000 μm, preferably between 1 μm and 100 μm, and it is especiallypreferred if the primary beam width is about 10 μm. When comparing theespecially preferred embodiments, the primary beam width is adjusted toabout 2 nm in the SEM mode and to about 10 μm in the SEEM mode, i.e. thebeam width is 5·10³ times larger in the SEEM mode than in the SEM mode.Thus, the apparatus can operate much faster in the SEEM mode than in theSEM mode because SEEM images thousands or even millions of pixels inparallel depending on the resolution of the detector.

Generally, the different primary beam widths in SEM and SEEM mode areprovided in that the aperture means 2 is formed as an aperture having adiameter in the range of 10 μm to 50 μm in the SEM mode of operation,and the aperture means is an aperture having a diameter in the range of100 μm to 200 μm in the SEEM mode of operation. However, a differentimplementation of such an aperture means 2 is provided by an aperturemeans which comprises the condenser lens 3. In this case, the condenserlens 3 is adapted to switch the beam width of said primary beam betweena width appropriate for serial imaging and a width appropriate forparallel imaging, This switching is accomplished by altering the focallength of the condenser lens 3. Therefore, it is not necessary to changeapertures in the case where the collimation of the primary beam isachieved by appropriate operation of the condenser lens.

One possible embodiment of an adjustable aperture is to provide at leasttwo different apertures, one having a diameter in the range of 10 μm to50 μm and one having a diameter in the range of 100 μm to 200 μm. Forexample, the apertures could be formed as small platinum disks ormolybdenum strips with holes. These at least two apertures are disposedon a lens aperture holder and can be centered by an aperture assemblywhich permits both X- and Y-centering of each aperture disk in thecolumn.

Another embodiment of the adjustable aperture means 2 is now describedwith reference to FIGS. 2 and 3. FIG. 3 shows the beam shaping section20 of the beam apparatus in the case where a so-called multi aperture isprovided. Several examples of such multi apertures and their respectivemodes of operation are described in EP 0 999 573 A1. For ease ofunderstanding, the condenser lens 3 is not shown in FIG. 3.

An embodiment of such a multi aperture is shown in FIG. 2, where multiaperture 21 is a circular flat disc having several beam definingopenings 21 a, 21 b with a specified diameter. According to the presentinvention, the openings 21 a, 21 b are divided into two differentgroups, namely one group 21 a having a width appropriate for serialimaging and a second group 21 b having a width appropriate for parallelimaging. Preferably, the diameters of the openings 21 a belonging to thefirst group are in the range of 10 μm to 50 μm, and the diameters of theopenings 21 b belonging to the second group are in the range of 100 μmto 200 μm. Before the beam passes through one of these openings, itgenerally has a diameter bigger than the diameter of the opening. Thus,the beam defining aperture only allows electrons to pass whose distancefrom the beam axis is smaller than the aperture diameter and eliminatesthe rest. The first deflection unit is capable of directing the beamthrough any one of the beam defining apertures 21 a, 21 b in multiaperture unit 21 thereby determining the beam diameter and,consequently, the current of the beam. The selection of a specific beamdefining aperture is the choice of the user and based on his intentions,namely the selection depends on whether the user intends to conduct aSEM or a SEEM mode inspection of the sample. In view of the presentinvention, it is not required to arrange beam defining apertures 21 a,21 b in a specific pattern on multi aperture unit 21. It is, however,preferred to have sufficient distance between outer rims of adjacentapertures so that electrons flying on the outmost trajectories of thebeam do not incidentally pass through neighboring apertures. On theother hand, the distances between outer rims of adjacent aperturesshould not be too wide. This permits deflections of the beam withsmaller angles since the center of beam defining apertures 21 a, 21 bare arranged closer to the center of multi aperture unit 21.Furthermore, it is preferred to have one beam defining aperture locatedin the center of multi aperture unit 21. If a certain applicationrequires the use of the center aperture, then it is not necessary todeflect the e-beam which can remain on the optical axis.

The operation of a multi aperture is now described with respect to FIG.3. Electron beam source 1 emits a beam of electrons towards multiaperture 21. Multi aperture 21 comprises several openings 21 a, 21 b ofdifferent size. A first deflecting unit 22 directs the beam of electronsthrough one of the beam defining apertures 21 a, 21 b and a seconddeflecting unit 23 directs the beam of electrons back to the opticalaxis. Second deflection unit 23 comprises two deflection stages 23 a and23 b. The beam, after having been delimited by one of the beam definingapertures 21 a, 21 b, diverges from the optical axis. In a first step,deflection unit 23 a redirects the beam and guides it back towards theoptical axis. At the point of intersection or, in case the beam does notintersect with the optical axis, at a point where the e-beam passes theoptical axis in close vicinity, deflection unit 23 b redirects the beamso that it propagates along the optical axis or in close vicinity to theoptical axis and more or less parallel to it. The expression “more orless parallel” within the meaning of this invention includes deviationsin which the beam still passes the objective lens close to its centerwithout causing excessive imaging artifacts.

The provision of a double stage second deflection unit 23 a and 23 bdisposes, in certain applications, the provision of a third deflectionstage, since the beam already propagates in a direction close to theoptical axis. Nevertheless, even in a beam column with a double stagesecond deflection unit 23 a and 23 b, it is in some applicationspreferred to have an additional double stage third deflection unit. Theprovision of such allows conducting a parallel shift of the e-beam.

Turning now back to FIG. 1, a condenser lens 3 is disposed above theaperture means 2. The effect of the field produced by the condenser lens3 is equivalent to an optical lens and symbolized by the lens-shapeddotted lines. Scanning means 4 are disposed below aperture means 3 fordeflecting the primary beam when scanning the sample 7. An objectivelens 5 is disposed below scanning means 4 for focusing the primary beam.Similar to condenser lens 3, the lens-shaped dotted lines denote theeffect of the field produced by objective lens 5. Typically, objectivelens 5 comprises an electrostatic portion as well as a magnetic fieldportion.

Finally, a sectorized detector 6 may be provided in all embodimentsaccording to the present invention. In the specific embodiment shown inFIG. 1, the detector 6 is ring-shaped and concentrically aligned withthe optical axis of the beam column. Detector 6 is disposed betweenobjective lens 5 and scanning means 4 for detecting secondary electronsemitted from sample 7. However, this arrangement is a mere example andthe detector 6 may have other shapes than ring-like, e.g. full circle orsquare shapes. Furthermore, detector 6 may also be disposed at otherpositions, e.g. below objective lens 5, or may even be not centeredaround the optical axis but disposed at a lateral position at the sideof the beam column. Preferably, sectorized detector 6 is a multichannelplate with sectorized anode. However, also other types of sectorizeddetectors can be used in the apparatus according to the presentinvention. Especially, an array of semiconductor diodes is preferred forthe sectorized detector. Reverse biased p-i-n diodes having a largei-region may be used as semiconductor detectors. Secondary electronsincident on a p-i-n diode generate electron-hole pairs in said i-regionwhich are detected by an analyzing circuitry.

Two different modes of operation of the embodiment shown in FIG. 1 arenow described with reference to FIGS. 4 and 5. FIG. 4 shows a first modeof operation, referred to as SEM mode, where the aperture means 2 isadjusted for collimating the primary beam to a width appropriate forserial imaging of a sample. Particle source 1 emits electrons within arelatively wide angle which is indicated by the dotted lines extendingfrom source 1. This relatively wide beam is collimated by the aperturemeans 2. Preferably, the adjustment of the aperture means 2 is done byapplying art aperture 2A having a diameter in the range of 10 μm to 50μm. Thus, the primary beam is blocked outside the opening of theaperture and only a collimated beam is allowed to pass the aperture.

The full lines in FIG. 4 show the beam path of the primary beam when thecondenser lens 3 is not in operation. The width of the primary beam isthen only geometrically determined by the diameter of the aperture 2A.Furthermore, the demagnification is solely determined by the spacingbetween source and objective lens and the spacing between objective lensand sample. A different possible beam path is shown by the dash-dottedlines in FIG. 1. This beam path is achieved by operating condenser lens3 as to collimate the primary beam and generate a crossover C. It may beadvantageous to use the latter mode of operation since it gives moreflexibility in demagnification which may be varied over magnitudes byappropriate adaptation of the condenser lens.

Objective lens 5 is adjusted to focus the primary beam on sample 7, i.e.to minimize the spot size of the primary beam on the sample. Typically,the primary beam width in the SEM mode is between 1 nm and 100 nm,preferably between 1 nm and 50 nm, and is especially preferably about 2nm. The sample 7 is then raster scanned using the scanning means 4,wherein the primary beam is directed to a respective position of asingle pixel on the sample 7. The arrows indicate secondary orbackscattered electrons emitted from the surface of the sample 7 andwhich are detected by the sectorized detector 6. Since in the SEM modeonly a single pixel is imaged at a time, the plurality of signalsproduced by the individual sectors of the detector 6 is merged to form asignal corresponding to the single pixel presently imaged. Thus, in SEMmode a serial imaging of the sample is conducted. The signalcorresponding to the single pixel may be a single signal, i.e. all thesignals of all individual sectors are merged into one signal, or may bea signal consisting of a few number of subsignals which are produced bymerging the signals of individual sectors belonging to specific subsets.As an example, there may be provided five subsets corresponding to thecenter and four quadrants. The advantage of providing such a spatiallyresolved signal for a single pixel is that topology information can beextracted from the signal. Nevertheless, it should be noted that even inthe case of a spatially resolved signal, only one pixel at a time isimaged in the SEM mode.

Summarizing the above, this allows to operate an apparatus according toan embodiment of the present invention in a SEM mode, i.e. the apparatusoperated according to the above method serves as a Scanning ElectronMicroscope. As mentioned above, this mode of operation allows forexcellent spatial resolution in sample imaging, but only relatively lowthroughput is achieved due to serial pixel processing: The narrow spotsize of the primary electron beam, typically about 2 nm diameter,defines the pixel region on the surface of the sample. Secondaryelectrons emitted from that region are detected by the sectorizeddetector wherein each sector has a corresponding signal channel. In theSEM mode, the signals of the individual sectors are merged into a singleor few output signals which represent the pixel momentarily imaged.Thus, the total detector surface is used for imaging a single pixel.

FIG. 5 shows a different mode of operation, referred to as SEEM mode,wherein the aperture means 2 is adjusted for collimating the primarybeam to a width appropriate for parallel imaging of a sample.Preferably, the adjustment of the aperture means 2 is done by applyingan aperture 23 having a diameter in the range of 100 μm to 200 μm, whichcould be preferably done by selecting an aperture 21 b having a largewidth of a multi aperture. This allows for a primary electron beam whichis wide enough for illuminating a relatively large portion of the samplesurface. Furthermore, when using a large aperture for the aperturemeans, a sufficient parallelity of the beam may be achieved.

Also in SEEM mode, condenser lens 3 may be in operation or not. As inFIG. 4, the full line shows the beam path without operation of condenserlens 3 and the dash-dotted line shows the beam path with theaforementioned operation of condenser lens 3. Objective lens 5 isoperated in a different way compared to SEM mode. Three typical modes ofoperation of objective lens 5 are indicated by roman numbers in FIG. 5.According to a first mode of operation of objective lens 5 which isindicated by dotted line I, the objective lens is operated in such a waythat an image of the aperture 2 is produced in the sample plane. Belowcrossover C′ the beam widens again and illuminates an area of width W onthe sample surface. The width W of this area depends on the focusingproperties of objective lens 5 and the spacing between objective lens 5and sample 7. The beam path in a second mode of operation is indicatedby dashed line II, where objective lens 5 is operated to focus theprimary beam in an plane at infinite distance. Thus, the primary beamincident on the sample is parallel and its width depends on the width ofthe primary beam at the entrance of objective lens 5. The beam path ofthe primary beam in a third mode of operation of objective lens 5 isindicated by dash-dotted lines III. In this third mode, objective lens 5is adjusted to focus the primary beam on a plane behind sample 7 but atfinite distance, such that the size W of the area on the sampleilluminated by the primary beam becomes large.

It should be understood that the focusing of the primary and secondaryelectrons is not independent from each other, but it is possible toachieve the same focusing in every one of the three aforementioned modesof operation. However, it may be necessary to adjust the relativepositions of the particle source, the objective lens and the detector tothis end. Alternatively, an intermediate acceleration voltage oradditional lenses, e.g. a second condenser lens, may be utilized toadjust the focusing of the primary and secondary electronsindependently.

Since the objective lens influences the behavior of both primary andsecondary electrons, it is not desirable to alter the parameters of theobjective lens during operation when switching between operation modes.Nevertheless, other elements of the apparatus can be operatedsubstantially independently to achieve the required operation mode.Especially, it is possible to control the spot size of the primary beamby adjusting the condenser lens 3. When the focal length of thecrossover produced between the condenser lens 3 and the objective lens 5is reduced, the spot on the sample 7 surface is narrowed. Vice versa, ifthe focal length of the crossover produced between the condenser lens 3and the objective lens 5 is increased, the spot on the sample surface iswidened. Therefore, the focal length of the crossover produced betweenthe condenser lens 3 and the objective lens 5 is increased in the SEEMmode and is reduced in the SEM mode.

Typically, the primary beam width in the SEEM mode is between 0.5 μm and1000 μm, preferably between 1 μm and 100 μm, and is especiallypreferably about 10 μm. Thus, the area illuminated in the SEEM mode ispreferably about 2.5·10⁷ times larger than the area illuminated in SEMmode.

Preferably, not the whole area illuminated is imaged as will bedescribed now with reference to FIG. 6. Primary beam 71 is produced bythe beam apparatus and has a width W at the surface of the sample 7.FIG. 6 further shows a magnified view of the imaging portion of beam 71on sample 7 as it is imaged by a sectorized detector. As can be seen,the relatively small area 71 at the surface of the sample is imaged on amuch larger detector area 61 of width W′. For facilitation ofunderstanding, detector area 61 is not depicted as a ring-shaped areabut as a simple full circle so that no difficulties due to differenttopologies of imaging area 71 and detector area 61 have to be taken intoaccount. Since the detector is sectorized, each sector 62 represents amuch smaller area 72 on the sample surface. Furthermore, typically notthe whole area 71 but only its central portion is imaged as is indicatedin FIG. 6. Thereby, edge effects can be eliminated as, e.g., imagedistortions due to non-uniformities in charge on the imaging surface:Typically, the sample surface areas at the edge of the beam 71 have lessuniform charge distributions than surfaces at the interior portion ofthe beam because there is no electron flux outside the circumference ofthe beam diameter.

As an example for the principle of spatial resolution with a sectorizeddetector, the sample 7 is imaged with a magnification of 2000. Then, ifthe area W on the sample surface is 10 μm, the width W at the detectorarea is 20 mm. If the detector is, e.g., sectorized in 100×100 elements62 of a dimension of 200 μm, each element represents a correspondingarea 72 of 100 nm dimension on the sample surface.

Going back to FIG. 5, secondary electrons emitted from the surface ofthe sample 7 are indicated by arrows. The secondary particles aredetected by the sectorized detector 6 and each of the plurality ofsignals produced by the individual sectors 62 of the detector 6represents a respective portion 72 of the sample surface. Thus, thespatial resolution in SEEM mode is determined by the magnification aswell as the number and size of the sectors 62 of the detector 6. Sincethe number of sectors 62 of the detector is high, e.g. 10,000 or higher,and all sectors 62 of the detector produce their own, individual signal,at least the center part of the illuminated sample surface area 71 isimaged in parallel. Thus, SEEM could also be called a multi-pixelimaging mode.

When operating in SEEM mode, the scanning means 4 are not necessarilyused: In the SEEM mode, the width of the primary beam is much largerthan in the SEM mode, but it may still be necessary to move the sample 7with respect to the beam to scan the sample. However, only mechanicalmovement of the stage 8 of the sample 7 with respect to the primary beamand not a scanning means 4 for electromagnetically steering the primarybeam may be used in SEEM mode. Furthermore, it may be desirable for aspecific application to provide a highly parallel beam which may beachieved by deflecting the beam as little as possible. Therefore, amovable stage 8 provides a good means for mechanically moving the samplerelative to the primary beam. On the other hand, the scanning means 4may also be used in SEEM mode. Especially, their operation is muchfaster than the mechanical operation of the movable stage. Also, thescanning means and the movable stage may be operated in combination.

Summarizing the above, the above described operational measures allow tooperate an apparatus according to an embodiment of the present inventionin a SEEM mode, i.e. the apparatus operated according to the aboveserves as a Secondary Electron Emission Microscope. In this mode, thesectorized detector is operated such that the signals stemming fromindividual sectors are separately processed in parallel. Thus, this modeof operation allows for high throughput due to parallel, multi-pixelimaging, but spatial resolution is not as high as in the SEM mode: InSEEM mode, spatial resolution is not defined by the narrow spot size ofthe primary beam as in the SEM mode, but by the sectorization of thedetector, i.e. the pixel size in the SEEM mode is dependent not only onthe spot size of the primary beam, but also on the magnification and onthe number of sectors of the detector. In the above example, each of the10⁴ individual sectors of the detector imaged a surface region of thesample with a diameter of 100 nm. When comparing the forestanding withthe description of the SEM mode above, the surface region of the samplecorresponding to a pixel is typically larger in the SEEM mode than thepixel region in the SEM mode. However, the massive parallel imaging ofthese larger pixel regions in the SEEM mode leads to a much higherthroughput as in the serial SEM mode. Furthermore, sufficient spatialresolution for the objects of SEEM is still achieved by use of asectorized detector.

FIG. 7 is a schematic view of a further embodiment of the presentinvention. The apparatus according to this embodiment comprisessubstantially the same elements as the first embodiment, namely aelectron source 1, aperture means 2, a condenser lens 3, scanning means4, an objective lens 5, a sectorized detector 6, and a stage 8 on whicha sample 7 is placed. Preferably, the aperture means 2 is an aperture 2Bhaving a diameter in the range of 100 μm to 200 μm. This allows for aprimary electron beam which is wide enough for illuminating a relativelylarge portion of the sample surface. Furthermore, when using a largeaperture 2B for the aperture means 2, a sufficient parallelity of thebeam may be achieved. As a main difference to the embodiment shown inFIG. 1, an additional light source 9 is provided in this embodiment ofthe invention.

The provision of a light source allows additionally for Photo-ElectronEmission Microscopy (PEEM) to be accomplished in the present embodimentof the invention. As has been already mentioned above, PEEM may lead topositive charge build-up on insulating surfaces. However, SEEM may leadto negative charge build-up for the aforementioned reasons. Therefore,the apparatus according to the present embodiment may be operated in acombined SEEM/PEEM mode when inspecting insulating surfaces. In thiscombined SEEM/PEEM mode, the effects of negative/positive chargebuild-up on insulating surfaces cancel each other and leave the surfacein a stable, substantially uncharged state. Thus, also very sensitivestructures may be inspected with a largely reduced possibility ofdamaging them. Also, other classes of materials show enhanced surfaceconductance induced by the light. The underlying mechanism of pairproduction of electrons and holes also allows for reduction ofaccumulated excess charge.

However, the arrangement of the light source 9 shown in FIG. 7 shouldnot be considered typical or limiting. Especially, the light source 9could, e.g., also be disposed above condenser lens 5. In this casephotons emitted by light source 9 would travel through theelectromagnetic field produced by condenser lens 5. However, this lensfield would not affect the uncharged photons but only the electronsemitted by source 1. Preferably, light source 9 is a mercury vapor lampemitting light in the spectral range of 200 nm to 600 nm wavelength.Light of a wavelength between 200 nm and 600 nm is relatively simple toproduce by the mercury vapor lamp. Furthermore, the light source 9preferably comprises a parabolic mirror which directs the light of thelamp onto the sample 7. Light of a wavelength between 200 nm and 600 nmis very difficult to focus by means of conventional lens optics. Aparabolic mirror allows for substantially parallel light beams also inthis range of wavelength. For some applications, parallelity of thelight beam is important for a homogeneous exposure and allows thereforefor images with better properties. If a parabolic mirror is consideredtoo expensive, the parabola may be approximated by intersecting mirrorplanes.

It is further preferred that the sample 7 is supported and moved by amovable stage. Although the width of both the primary beam and the lightbeam is relatively large, it may still be necessary to move the samplewith respect to the beam to scan the sample. However, SEEM/PEEM mayrequire mechanical movement of the stage of the sample with respect tothe primary beam, since it may not be desirable to have additionaldeflecting means for the light beam, especially when taking into accountthat light at the typically used wavelengths of 200 nm to 300 nm isdifficult to deflect by conventional optics. Furthermore, it may bedesirable for some applications to provide highly parallel beams whichmay be achieved by deflecting the beams as little as possible. In thesecases, a movable stage provides a good means for mechanically moving thesample relative to the primary beam and the light beam. However, as hasbeen described above, also the scanning means may be used for deflectingthe primary beam so that one may take advantage of their superior speedcompared to the mechanical movement of the movable stage.

Preferably, all apparatuses in accordance with the present invention mayfurther comprise blanking means for blanking the primary beam ofelectrons.

The blanking means can blank the primary beam in case it is desired tohave no electron beam incident on the sample. Otherwise, i.e. withoutthe blanking means, the source of electrons would have to be turned offis this case. Due to the blanking means, it is not necessary to turn offthe electron source if a pure PEEM mode operation of the apparatus isdesired. Accordingly, the lifetime of the source is not negativelyinfluenced by subsequently switching it on and off. Furthermore, it ispossible to switch between SEEM or SEEM/PEEM modes and a pure PEEM modevery quickly since the primary beam has only to be blanked or unblankedby the blanking means.

Preferably, the blanking means are formed by a pair of electrodes whichdeflect the primary beam away from the axis of the column. Furthermore,an aperture is disposed in the path of the deflected beam so that thebeam is not incident on the sample surface. It is especially preferredto use the aperture for collimating the primary beam also as an aperturefor the blanking means. Another possibility of forming the blankingmeans can be provided if the particle source is formed by field emissioncathodes, i.e. an array of emitter tips. In this case, the blanking maybe effected by reducing the extraction voltage applied between theemitter tip and the gate electrode. Since the beam current of an emittertip depends almost exponentially on the extraction voltage, a reducedextraction voltage leads to a considerably reduced beam current which,in result, has the same effect as blanking the beam by theaforementioned electrodes.

FIG. 8 shows one of the embodiments of the invention described inconnection with FIG. 7 in a first mode of operation, referred to ascombined SEEM/PEEM mode hereinafter. In this combined SEEM/PEEM mode,the electron beam apparatus is operated in the SEEM mode describedabove, i.e. a large aperture 2B is chosen and the condenser lens 3 isadjusted as to widen the primary beam. Additionally, in the combinedSEEM/PEEM mode, the light source 9 is operated as to emit light of ashort wavelength onto sample 7. Preferably, the area illuminated by theprimary beam and the light beam at the sample surface are substantiallythe same. It is further preferred that the spots of the primary beam andthe light beam at the sample surface coincide substantially.

All of these operational measures allow to operate an apparatusaccording to an embodiment of the present invention in a combinedSEEM/PEEM mode, i.e. the apparatus operated according to the abovemethod serves as a Secondary Electron Emission Microscope as well as aPhoto-Electron Emission Microscope. In this mode, the sectorizeddetector is operated such that the signals stemming from individualsectors are separately processed in parallel. Both the SEEM and PEEMmodes reveal different information about the sample which may becollected simultaneously in this combined SEEM/PEEM mode.

Preferably, the electron beam and the light beam are adjusted to canceleach others respective charge build-up in the combined SEEM/PEEM mode.As has been already mentioned above, SEEM may lead to a negative chargebuild-up of the sample surface in case fewer secondary electrons areemitted than primary electrons are collected by the sample 7. Also, ithas been described that PEEM may lead to a positive charge build-up oninsulating surfaces since the electrons emitted due to the photo-effectare not replaced. Therefore, the negative and positive charge build-upsof SEEM and PEEM can be counterbalanced by applying both modes ofoperation simultaneously and adjusting the intensity of the light beamand the beam current of the primary beam such that the electronsdeposited by the primary beam substantially equal the number ofelectrons removed by the photo-effect. Thus, a substantiallyelectrically neutral and stable state of the sample surface can beachieved and damage to the sample due to charge build-up can be avoided.

As has been discussed above, the reduction of unwanted charge build-upcan be prevented by the combined SEEM/PEEM mode also for another classof materials where the above mechanism does not work. For thesematerials excitons are produced by the incident light of the lightsource. Accordingly, the surface conductance may increase since theelectrons or holes, although in a quasi-bound state, contribute toenhanced charge transport in the sample. Thus, charge build-up caused bySEEM inspection can be transported away from the illuminated area. Alsoby this mechanism a substantially electrically neutral and stable stateof the sample surface can be achieved and damage to the sample due tocharge build-up can be avoided.

FIG. 9 shows one of the embodiments of the invention described inconnection with FIG. 7 in a further mode of operation, referred to asPEEM mode hereinafter. In this pure PEEM mode light from a light source9 is directed to the sample 7, but the blanking means 10 is used forblanking the primary beam. In this embodiment, the blanking means 10 areformed by a pair of electrodes. The electrical field applied between theelectrodes deflects the primary beam away from the axis of the columnand onto aperture 2B. Thus, the primary beam does not reach sample 7.Blanking means 10 blank the primary beam in case it is desired to haveno electron beam incident on the sample. Otherwise, i.e. withoutblanking means 10, the source 1 of electrons would have to be turned offis this case. Especially, when switching to a pure PEEM mode or whenswitching between SEM/SEEM and PEEM modes the blanking means 10 allowfor fast switching since the electron source 1 is not altered inoperation.

The above operational measures allow to operate an apparatus accordingto an embodiment of the present invention in a PEEM mode, i.e. theapparatus operated according to the above method serves as aPhoto-Electron Emission Microscope. In this mode, the sectorizeddetector is operated such that the signals stemming from individualsectors are separately processed in parallel. Thus, this mode ofoperation allows for high throughput due to parallel, multi-pixelimaging, but spatial resolution is not as high as in the SEM mode: Thespatial resolution is not defined by the narrow spot size of the primarybeam as in the SEM mode, but by the sectorization of the detector as inthe SEEM mode. As an example, the light of a mercury vapor lamp is usedwhich has a wavelength between 200 nm and 600 nm and is relativelysimple to produce. More advanced applications may use radiation from asynchrotron.

Also in the pure PEEM mode it may still be necessary to move the samplewith respect to the beam to scan the sample. However, PEEM requiresmechanical movement of the stage of the sample with respect to theprimary beam, since it is not desirable to have additional deflectingmeans for the light beam, especially when taking into account that lightat the typically used wavelengths of 200 nm to 300 nm is difficult todeflect by conventional optics. Furthermore, it is desirable in PEEM toprovide a highly parallel beam which may be achieved by deflecting thebeam as little as possible. Therefore, a movable stage provides a goodmeans for mechanically moving the sample relative to the light beam.

In another embodiment of the present invention, an objective lens of aelectron beam apparatus for focusing said condensed primary beam isadapted to switch between a focus forming an image of the particlesource in a plane of a surface of a sample to be serially inspected anda focus forming an image of an aperture in a plane of a surface of asample to be parallel inspected. It is especially preferred that theobjective lens has a control means which allows for fast and easyswitching between the two inspection modes.

The above electron beam apparatus may be operated in that a primary beamof electrons is generated by said particle source, collimating by saidaperture, and focused by said objective lens. For operation in SEM mode,the objective lens is adjusted to form an image of the particle sourcein the focal plane, wherein the objective lens is adjusted to form animage of said aperture in the focal plane when the apparatus is operatedin SEEM mode.

In summary, all the apparatuses according to an embodiment of thepresent invention allow a user to switch between different modes ofsample inspection:

A user can inspect a sample in a single-pixel imaging mode by selectingan aperture of a small width for collimating a beam of electrons,scanning said sample using deflection means, and detecting secondaryelectrons by means of a detector, wherein signals produced by individualsectors of said detector are superimposed to generate a single or fewoutput signals corresponding to a single pixel on the sample surface.

Further to the above, a user can also inspect a sample in a multi-pixelimaging mode by selecting an aperture means of a large width to producea large diameter beam of electrons, directing the beam to an inspectionregion on the sample surface, and detecting secondary electrons in asectorized detector, wherein each sector of said detector produces asignal indicative of a corresponding inspection area on said samplesurface.

According to a further embodiment of the present invention, a user mayalso inspect a sample in a dual multi-pixel imaging mode by selecting anaperture means of a large width to produce a large diameter beam ofelectrons, producing a light beam, directing said large diameter beam ofelectrons and said light beam to a substantially coinciding inspectionregion on the sample surface, and detecting secondary particles by meansof a sectorized detector, wherein each sector of said detector producesa signal indicative of a corresponding inspection area on said samplesurface.

1. A charged particle beam apparatus, comprising: a charged particlesource for producing a primary beam of charged particles, a condenserlens for shaping said primary beam of charged particles; beam shapingmeans for collimating said primary beam of charged particles; whereinsaid beam shaping means is adapted to switch between a collimation ofsaid primary beam resulting in a width appropriate for serial imagingand a collimation of said primary beam resulting in a width appropriatefor parallel imaging; scanning means for deflecting said primary beam ofcharged particles; and a sectorized detector for detecting secondarycharged particles.
 2. The apparatus according to claim 1, wherein saidprimary beam width appropriate for serial imaging is between 1 nm and100 nm.
 3. The apparatus according to claim 1, wherein said primary beamwidth appropriate for parallel imaging is between 0.5 μm and 1000 μm. 4.The apparatus according to claim 1, wherein the beam shaping meanscomprises an objective lens for focusing said primary beam, wherein saidobjective lens is adapted to switch between forming an image of saidcharged particle source in a plane of a surface of a sample to beserially inspected and forming an image of an aperture means in a planeof a surface of a sample to be parallel inspected.
 5. The apparatusaccording to claim 1, wherein said beam shaping means comprises saidcondenser lens and said condenser lens is adapted to switch the beamwidth of said primary beam between a width appropriate for serialimaging and a width appropriate for parallel imaging.
 6. The apparatusaccording to claim 1, wherein said beam shaping means is an aperturehaving a diameter in the range of 10 μm to 50 μm in the case of serialimaging, and wherein the beam shaping means is an aperture having adiameter in the range of 100 μm to 200 μm in the case of parallelimaging.
 7. The apparatus according to claim 1, wherein said sectorizeddetector is a multichannel plate with sectorized anode or an array ofsemiconductor detectors.
 8. The apparatus according to claim 1, furthercomprising a movable stage for supporting and moving a sample.
 9. Theapparatus according to claim 1, further comprising a light source forproducing a light beam.
 10. The apparatus according to claim 9, whereinthe wavelength of the light produced by said light source comprises therange of 200 μm to 300 μm.
 11. The apparatus according to claim 9,wherein the light source further comprises means for forming a parallellight beam.
 12. The apparatus according to claim 9, further comprisingblanking means for blanking said primary beam of charged particles. 13.A method for operating the charged particle beam apparatus according toclaim 9, wherein the method of operation of the charged particle beamapparatus is switched in operation between at least two of modes SEM,SEEM, PEEM or SEEM/PEEM.
 14. A method for serially operating a chargedparticle beam apparatus having a charged particle source for producing aprimary beam of charged particles, a condenser lens for shaping theprimary beam of charged particles, a beam shaping means adapted toswitch between a collimation of the primary beam to a width appropriatefor serial imaging as well as a collimation of the primary beam to awidth appropriate for parallel imaging, a scanning means for deflectingsaid primary beam of charged particles, and a sectorized detector fordetecting secondary charged particles, the method comprising: providingthe charged particle beam apparatus; adjusting the beam shaping meansfor collimating the primary beam of charged particles to collimate saidprimary beam of charged particles to the width appropriate for serialimaging of a sample, scanning said sample using the scanning means,wherein said primary beam of charged particles is directed to arespective position of a single pixel on said sample, and detectingsecondary charged particles by means of the sectorized detector, whereinsignals produced by individual sectors of said detector are merged toform a signal corresponding to said single pixel.
 15. A method foroperating a charged particle beam apparatus having a charged particlesource for producing a primary beam of charged particles, a condenserlens for shaping the primary beam of charged particles, a beam shapingmeans adapted to switch between a collimation of the primary beam to awidth appropriate for serial imaging as well as a collimation of theprimary beam to a width appropriate for parallel imaging, a scanningmeans for deflecting said primary beam of charged particles, and asectorized detector for detecting secondary charged particles, themethod comprising: providing the charged particle beam apparatus;adjusting the beam shaping means for collimating the primary beam ofcharged particles to collimate said primary beam of charged particles tothe width appropriate for parallel imaging of a sample; directing saidprimary beam of charged particles to a predetermined position on saidsample; and detecting secondary charged particles by means of thesectorized detector, wherein the signals produced by individual sectorsof said detector are individually collected.
 16. A method for operatinga charged particle beam apparatus having a charged particle source forproducing a primary beam of charged particles, a condenser lens forshaping the primary beam of charged particles, a beam shaping meansadapted to switch between a collimation of the primary beam to a widthappropriate for serial imaging as well as a collimation of the primarybeam to a width appropriate for parallel imaging, a scanning means fordeflecting said primary beam of charged particles, and a sectorizeddetector for detecting secondary charged particles, the methodcomprising: providing the charged particle beam apparatus, adjusting thebeam shaping means for collimating the primary beam of charged particlesto collimate said primary beam of charged particles to the widthappropriate for parallel imaging of a sample, producing a light beam,directing said primary beam of charged particles and said light beam toa predetermined position on said sample, and detecting secondary chargedparticles by means of the sectorized detector, wherein the signalsproduced by individual sectors of said detector are individuallycollected.
 17. The method according to claim 16, wherein the chargedparticle beam and the light beam are adjusted to cancel a chargebuild-up on the sample surface.
 18. The method according to claim 16,wherein the primary beam of charged particles is blanked by blankingmeans.
 19. A method for operating a charged particle beam apparatuscomprising a charged particle source for producing a primary beam ofcharged particles, a condenser lens for shaping the primary beam ofcharged particles, a beam shaping means adapted to switch between acollimation of the primary beam to a width appropriate for serialimaging as well as a collimation of the primary beam to a widthappropriate for parallel imaging, a scanning means for deflecting saidprimary beam of charged particles, and a sectorized detector fordetecting secondary charged particles, said method comprising:generating a primary beam of charged particles by said particle source;collimating said primary beam by an aperture; and focusing saidcollimated primary beam by said objective lens, wherein said objectivelens is adjusted to form an image of said aperture in the working planeof said objective lens.